1. Field of the Invention
The present invention generally relates to a method of forming ruthenium (Ru) films for metal wring structures that can be used favorably in producing fine semiconductor devices.
2. Description of the Related Art
Ru films are drawing the attention because by forming a Ru film at the interface of Cu and barrier metal in a Cu wiring structure, which is the mainstream wiring structure used with high-speed logic devices such as MPUs, the Ru film can provide improved adhesion with Cu and thus significantly improve the reliability of wiring. Methods to form a Ru film on a TaN film or WN film, which is a Cu diffusion barrier metal, and then form a Cu film on top of the Ru film, are being examined (refer to C-C Yong et al., IITC 2006, pp. 187-189, “Physical, Electrical, and Reliability Characterization of Ru for Cu Interconnects” for an example of such method on a Ru/TaN combination). Specifically, application of a Cu liner consisting of a layered structure of Ru/TaN, etc., is examined.
A Cu liner film, such as Ru/TaN, which is being examined for use as a Cu wiring liner, tends to produce higher Cu wiring resistance if the film is thicker, because a thicker film results in a smaller Cu wiring volume. This creates a need to make the film as thin as possible. In a layered structure consisting of a copper-diffusion barrier film and a Ru film, however, making the Ru film thinner virtually prevents formation of a continuous film, resulting in the barrier film being exposed partially. As a result, an interface of Cu wiring and barrier film is produced, which can cause problems. If the Ru film is made thicker to form a continuous film, on the other hand, the Cu wiring resistance increases. In other words, formation of a thin, continuous Ru film is desired. Also, when forming a Ru film on a copper-diffusion barrier film such as a TaN film, TaNC film, etc., the Ru film is required to be formed in a reducing atmosphere to prevent the aforementioned barrier film from being oxidized.
According to US2006/0177601A, a Ru film can be formed in a reducing atmosphere by means of a step to supply a Ru material that contains a ligand containing a cyclopentadienyl group, and a treatment step using NH3 gas activated by high-frequency waves.